1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a secondary battery that improves reliability by preventing a mold resin part from being twisted and bent. A protrusion is formed either on a top edge of a side wall of a can of the battery or on an edge of an upper plane of a cap plate that covers the can of the battery. The protrusion adheres to the mold resin part, and supports the mold resin part to prevent mechanical distortion that is caused by external force.
2. Description of the Related Art
A secondary battery is a battery capable of repeatedly being charged and discharged for several times, which is different from a first battery that can not be charged. The secondary battery has been broadly used for an electronic device, such as a cellular phone, a notebook computer, a camcorder, and others.
An output voltage of a lithium secondary battery is typically 3.6 volt, which is three times higher than an output voltage of a nickel-cadmium battery or a nickel-hydrogen battery that has been often used as a power source of electronic equipments. The lithium secondary battery has higher energy density per unit weight than the nickel-cadmium battery or the nickel-hydrogen battery. Therefore, the use of the lithium secondary battery has been rapidly increased.
The lithium secondary battery mainly uses a lithium-based oxide as a cathode active material, and a carbon material as an anode active material. Further, the lithium secondary battery has been manufactured in various shapes such as a cylindrical shape, a polygon shape, a pouch shape, and others.
Among them, a polygon-shaped secondary battery includes a bare cell, a protection circuit board, and a mold resin part. The bare cell includes an electrode assembly, a can that accommodates the electrode assembly, and a cap assembly that is attached to an opening formed on the top of the can. The cap assembly includes a cap plate that covers the top of the electrode assembly.
The protection circuit board includes a protection circuit that protects the battery from being overcharged or over-discharged during charging/discharging process. The protection circuit board can be electrically connected to both electrodes of the bare cell through a lead plate or others.
The mold resin part is formed by filling a space between the cap plate of the bare cell and the protection circuit board with hot melted resin, followed by solidification. The mold resin part prevents battery components, which are placed between the cap plate and the protection circuit board, from being dislocated or being distorted.
A holder may be positioned at a portion of the upper surface of the cap plate in order to improve the connection between the cap plate and the mold resin part. The holder prevents a dislocation of the mold resin part from the cap plate by external force, such as twist and bend, and also prevents the mold resin part from being separated from the cap plate.
The holder has a shape of a simple rectangular parallelepiped. A protrusion formed on the upper surface of the cap plate is inserted into a groove formed on the bottom surface of the holder in order to fix the holder to the cap plate.
The battery, however, has various components that should be installed in a space between the cap plate and the protection circuit board, where the mold resin part is filled. For example, an electrolyte inlet and a stopper can be positioned in the space. A vent can be formed in the space to secure battery stability. A thermal breaker or a positive temperature coefficient (PTC) element can be placed in the space. A lead plate can be placed in the space to electrically connect two connection terminals of the protection circuit board to each other. As a result, the space, in which the holder is installed, is remarkably limited.
Accordingly, the size of the holder is also limited, and thus the connection between the cap plate and the mold resin part is not strong enough to resist external forces. Consequently, the loose connection causes problems that the position of the mold resin part changes relatively from the cap plate or the mold resin part is separated from the cap plate. Furthermore, additional time and cost for manufacturing the holder are required, which causes an increase in overall manufacturing cost.